Paper products such as paper towels and toilet tissue are widely used on a daily basis for a variety of household needs. Typically, such products are formed of a fibrous elongated web which is packaged and sold in rolls. Perforations are provided between sheets of the web to allow the user to conveniently separate a desired portion from the roll for use. In forming the web, very small grains or fibers produced in a pulping process are bonded together to form an elongated web. The fibers tend to extend in the longitudinal direction, and therefore in the bonding process the fibers are bonded somewhat end-to-end in the longitudinal direction of the sheet, while the fibers are somewhat side-by-side in the transverse web direction. Thus, the web generally has a greater tensile strength in the longitudinal or lengthwise direction since the fiber bonds are somewhat offset and the strength of the fibers plays a greater role in providing tensile strength in the lengthwise direction as compared to the width or transverse direction in which the strength of the bond between the adjacent fibers forms a larger component of the tensile strength.
The greater strength in the longitudinal direction is advantageous in that the sheets are generally fed in the longitudinal direction such that the tensile loads incurred during forming and handling the more easily handled by the web. However, often this can lead to problems in consumer use and the consumer's perception of the product. For example, with the greater strength in the longitudinal direction, often it becomes difficult to tear the product evenly at the perforations when the consumer is removing a desired portion from the product roll. Generally, such paper products are mounted on a dispenser and the consumer will utilize one hand to rip one or more towels from the roll. Often the towel will tend to rip along the lengthwise direction instead of tearing evenly along the perforations, due to the increased tensile strength in the longitudinal direction compared to the transverse direction. In use, the paper will often fail due to the lower tensile strength in the width direction (resulting for example in tearing in the longitudinal direction), such that the public will perceive the towel as generally weaker or defective and the consumer confidence is thereby diminished.
To overcome the perception of weakness, the overall strength of the towel may be made stronger, however this results in an even further increase in the strength in the longitudinal or machine direction of the towel with the towel becoming more costly; and the problem in separating the towel from a roll during dispensing is not solved. Thus, it is desirable to form a paper product having tensile strengths in the longitudinal (machine) and transverse (cross-machine) directional which are substantially equal or more nearly equal as compared to the conventionally formed paper web.
Fibrous webs are typically embossed to increase the bulk of the tissue and improve the absorbency, softness and appearance of the product both as individual sheets and in providing a uniform attractive roll package. To provide a uniform and attractive package, previous embossing techniques have been utilized to insure that the embossments of adjacent layers of the roll do not nest. For example. U.S. Pat. No. 4,803,032 to Schulz discloses a method for embossing a porous sheet which results in a uniform roll by preventing nesting of embossments of successive layers of the roll. As disclosed in the Schulz patent, fibrous sheet products produced on a paper making machine are non-uniform in tensile strength. Such fibrous products have a greater tensile strength in the machine direction (i.e., the longitudinal direction or the direction in which the sheet is fed) than in the cross-machine direction. Thus embossments have been utilized to improve the appearance and absorbency, but have not been recognized as a solution to the problem in providing a fibrous sheet product in which the tensile strengths are more nearly equal in machine and cross-machine directions.
U.S. Pat. No. 3,544,420 to Murphy et al. discloses a creped tissue product for various applications, with the object of the invention to increase the strength of the tissue. Murphy et al. recognizes that the tissue products are particularly weak in the cross-machine direction, and increases the strength of the tissue by utilizing embossment to interlock two or more superposed webs, with the lines or creping at an angle to the longitudinal and transverse directions of the assembled web. Murphy et al. achieves more uniform strength characteristics by disposing superposed stock web layers with the longitudinal directions angled with respect to each other and with both layers angled with respect to the longitudinal edges of the composite. Thus, the strength in the machine and cross-machine directions of the composite each have components of the machine and cross-machine strengths of the stock web components. While such an arrangement provides more uniform strength characteristics, forming of such a composite web requires spiral winding of the stock web which greatly complicates the web forming process. Such an arrangement is not suitable for forming relatively inexpensive, cost competitive paper products such as paper towels and toilet tissue.
U.S. Pat. No. 4,191,609 to Trokhan discloses an absorbent paper sheet and manufacturing method therefor, in which the paper is formed to have an array of uncompressed zones staggered in both the machine and cross-machine directions. In the paper forming operation, prior to the final drying, a network of picket-line-lineaments are imprinted on the embryonic web, with the lineaments including alternately spaced areas of compacted fibers and non-compacted fibers. When creped, the paper provides a relatively high bulk sheet having an improved cross-machine direction to machine direction stretch ratio. However, the Trokhan arrangement complicates the paper forming process and moreover sine the strength of the paper is determined during the initial forming, the Trokhan method does not realize the advantage of having an increased machine direction strength during forming and feeding of the web.